Kumar said that he had always wondered how a man who "ruined" Bihar for 15 years was "doing exceedingly well" on becoming the railway minister and receiving appreciation from even the prime minister.
Alleging that Prasad had "hoodwinked and misled" the nation and the people, Kumar, a former railway minister, said it was "the biggest-ever offence" committed by any public servant in office since Independence.
"Prasad owed an explanation to the nation and people," Kumar said, adding the RJD supremo should apologise to the nation.
"A person who earned laurels and sobriquets of being a management guru and was invited by several management institutions in India and abroad for lectures for hollow claims of the turnaround by the Railways stands exposed now," Kumar claimed.